During for example surgery, such as chest cavity surgery, a patient usually loses large amounts of blood. One way of dealing with this problem is to remove the lost blood and give the patient a transfusion of donated blood, to make up for the lost blood. Such donations are however accompanied with a plurality of problems, such as rejection of the donated blood, and the risk for spreading diseases.
In order to overcome these problems, it has been proposed in the prior art to collect blood lost from the patient and return this blood to the circulatory system of the patient. This is referred to as autologous blood transfusion. A transfusion unit according to the prior art is disclosed in FIGS. 1a and 1b. This transfusion unit comprises a blood bag, which has an inlet in an upper part of the bag and an outlet in the lower part of the bag. Within the blood bag, a main filter is integrated, so that blood that is entered into the blood bag is filtered. This filtration is essential in autologous blood transfusion, since it removes impurities, such as thrombi and tissue fragments in a wound. After filtration, the blood is collected in the bottom of the blood bag until it is to be retransfused. In this collection position (FIG. 1a), the outlet from the bag is blocked by means of a clamp or the like. When the blood is to be retransfused (FIG. 1b), a transfusion set is connected to the outlet of the bag. Thereafter the clamp is removed, and the transfusion set filter is primed and all air is expelled from the tubing before the transfusion set being connected to a cannula or the like in the patient and blood is retransfused into the patient. The transfusion set may be equipped with a blood filter in order to remove any blood clots or the like which may develop when storing the blood in the blood bag.
However, the prior art device described above have a plurality of disadvantages. First, the main filter is integrated in the blood bag, which means that only special blood bags may be used for this purpose. Moreover, these blood bags are quite complicated, and hence quite costly to manufacture. Moreover, as the blood bag is filled with blood, there is a risk that the level of blood may rise so that the stored blood is in contact with the filter while stored, which may decrease the quality of the stored blood.